Clamping devices of this type are sufficiently known and in use, so that there is no need for any particular printed documentation therefor. Such clamping devices are needed to clamp workpieces for working on them on tables of working machines, more particularly to clamp car body parts or like sheet metal in position to weld them together. The operation of the clamping arms on these devices is usually performed with actuator cylinders. The actuator cylinders operate by pneumatic pressure acting on one side or the other in order to bring the clamping arm, on the one hand, into a closing position and, on the other hand, into an opening position. The pressure medium terminals are mounted laterally of the flanges which form the ends of the cylinder, i.e., the pressure medium reset-line in particular extends laterally along the entire length of the adjusting cylinder. Depending on the type of sensors used (a magnetic field switch or a proximity switch), for the determination of the end position the same is applicable, i.e., these sensors are placed either on the mounting head of the device or laterally in the region of the actuator cylinder, the guide for the line also extending laterally of the device. Mechanically functioning roller feeler switches, operating uninfluenceds by electromagnetic influences from the outside, can practically not be used in such devices because there is usually too little space available in the region of the mounting head. The lateral feed of the pressure medium lines to the respective ends of the actuator cylinder and the cable line to the sensors, which is also positioned at one side of the device, are regarded as a particular disadvantage of such devices. On the one hand, it has to be taken into account that there is very often extremely limited space for the installation of such devices so that the outside guidance of the lines can be hindering. Furthermore, such lateral line guidances are naturally exposed to outside impairments and damages.